This study is trying to find the co-opetition basic strategy among domestic similar companies and focus on the strategy system of the formation of complementary advantages force and competitive energy when the China national petroleum corps in opening up the international market. With the obviously increasing dependence on petroleum in China and the entering of advanced international petroleum companies in China's market, the competition in petroleum industry becomes more serious than before. The cooperation and competition mode among national petroleum companies is an efficient way to push the development of petroleum industry in China. Based on the analysis of encountering difficulties in national petroleum industry, the necessity of co-opetition among national petroleum companies was proposed in this study. Moreover, basic orientation and path for co-opetition are analyzed. At last, the co-opetition for exploiting international petroleum market is proposed in this study.